Crystalline composition of lysine and succinic acid or alkali metal salt thereof

ABSTRACT

A crystalline salt of lysine hydrochloride, succinic acid or alkali metal salt, wherein the molar ratio of lysine to succinic ion calculated as succinic acid is between about 3 and 10. The salt has the appearance of ordinary table salt crystals.

Government Rights--This application was funded under USDA Contract No.90-34189-5014, Sub of 4051. The U.S. Government has certain rights underthis application and any patent issuing thereon.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a crystalline composition of lysine andsuccinic acid or an alkali metal salt of succinic acid. In particular,the present invention relates to the crystalline salt having a molarratio of lysine to the succinic ion calculated as the acid between about3 and 10 and to a process for preparing the crystalline composition. Thecrystalline composition is useful as a substitute for sodium chlorideused as a table salt in foods.

(2) Description of Related Art

The prior art has described various table salt substitutes. Illustrativeare U.S. Pat. Nos. 151,874,055 to Liebrecht; 2,824,008 to Perri et al;2,829,056 to Kemmerer; 3,015,567 to Hause et al; 3,993,795 to Mauror etal; 5,145,707 to Lee; 5,173,323 to Omari; 5,176,934 to Lee and 5,229,161to Turk. Turk describes salts of lysine and succinic acid wherein themolar ratio is 2 to 1 lysine to succinic acid which are essentiallyamorphous. British Patent No. 1,154,926 also describes various salts ofsuccinic acid and lysine in a 1 to 1 mixture. The problem with theseprior art salts is that they are not crystalline in form as is tablesalt and thus is not readily accepted on various foods such as pretzels,bagels or the like. Many substitutes also possess off flavors that areundesirable.

OBJECTS

It is therefore an object of the present invention to provide a novellysine and succinic acid or succinic alkali metal salt composition whichis crystalline in form and possesses a desirable salty flavor. Further,it is an object of the present invention to provide a process forforming the composition. These and other objects will becomeincreasingly apparent by reference to the following description.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is the X-ray powder diffraction pattern of lysine monohydrate.

FIG. 2 is the X-ray powder diffraction pattern of lysinemonohydrochloride.

FIG. 3 is the X-ray powder diffraction pattern of succinic acid.

FIG. 4 is the X-ray powder diffraction pattern of the product of Example1.

FIG. 5 is the X-ray powder diffraction pattern of the product of the2:1:1:0 example of Turk.

FIG. 6 is the X-ray powder diffraction pattern of the product of Example2.

FIG. 7 is the X-ray powder diffraction pattern of sodium chloride.

FIG. 8 is the X-ray powder diffraction pattern of the product of Example3.

FIG. 9 is the X-ray powder diffraction pattern of the product of the2:2:1:1 example of Turk.

FIG. 10 is the X-ray powder diffraction pattern of the product ofExample 4.

FIG. 11 is the X-ray powder diffraction pattern of the product ofExample 5.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a crystalline composition having theempirical formula

    Lys.sub.a Cl.sub.b Succ.sub.c X.sub.d

wherein Lys is L-lysine, Succ is succinic ion and X is selected from thegroup consisting of a sodium ion and a potassium ion and mixturesthereof, wherein a is about 3 to 10, wherein b is approximately the sameas a, c is 1 calculated as succinic acid, and d is 0 to 2.

Further the present invention relates to a process for the preparationof a crystalline composition having the empirical formula:

    Lys.sub.a Cl.sub.b Succ.sub.c X.sub.d

wherein Lys is L-lysine, Succ is succinic ion and X is selected from thegroup consisting of a sodium and a potassium ion and wherein a isbetween about 3 to 10, wherein b is approximately the same as a, c is 1calculated as succinic acid, and d is 0 to 2 which comprises: admixinglysine hydrochloride and a succinate compound selected from the groupconsisting of succinic acid and alkali metal salts thereof in a molarratio of Lys to Succ calculated as succinic acid of about 2:1 in anaqueous solution until solution is near saturation; heating the solutionat a temperature between about 60° C. and 80° C. and at a reducedpressure (preferably 25 in-Hg) such that water is removed from thesolution; cooling the solution so that the crystalline compositionprecipitates from the solution; and separating the crystalline salt fromthe solution, preferably by vacuum filtration.

The lysine (Lys) must be present in a molar ratio of between about 3 to10 to succinic ion calculated as succinic acid which is important toforming the crystals. Preferably a mixture of lysine monohydrochlorideand lysine monohydrate is used. The reason for this is not understoodsince one mole of succinic acid can form a salt with two moles of lysineas described in Turk.

The preferred alkali metal ion is potassium, since it contributes nosodium ion to the crystalline salt of the present invention. Mono- ordi-alkali metal salts of succinic acid can be used. The salts are formedby reacting an alkali metal base with succinic acid.

Lysine hydrochloride, preferably as the monohydrochloride, is used asthe starting material, thus contributing chloride ion to the crystallineproduct. The chloride ion is necessary to the formation of thecrystalline composition.

The solution is heated to between about 60° C. to 80° C. preferably 70°C. and then cooled the cooling is to about 30° C. or lower.

The salts are prepared from aqueous solutions with varying compositions.The nomenclature used to describe the solution composition is a seriesof molar ratios, i:j:k:l, wherein i is moles of L-lysine, j is moles ofchloride ion, k is moles of succinic acid, and 1 is either moles ofsodium or potassium.

EXAMPLE 1

Solution Composition--2:1:1:0, Sodium/Potassium Free

10 grams of L-lysine monohydrochloride and 8.95 grams of L-lysinemonohydrate were dissolved in 25 ml of water. 6.5 grams of succinic acidwere added and dissolved. The resulting solution was placed in adistillation unit with variable reflux. The solution was heated to 70°C. while being stirred. The temperature of solution (58° C.) and vacuum(25 mm of Hg) were maintained until about 40% of the water (10 grams)was collected as condensate. The resulting solution was cooled to roomtemperature resulting in crystallization. The slurry was filteredthrough a 5-10 micron filter; the retained solids was the crystallineproduct. Elemental analysis was performed on two samples of thecrystalline product wherein sample 1 had twice the 10 cooling time ofsample 2 and the results are given in Table 1.

                  TABLE 1                                                         ______________________________________                                        Elemental analysis of Example 1. Solution composition-2:1:1:0                           sample 1 (wt. %)                                                                         sample 2 (wt.%)                                          ______________________________________                                        carbon      34.54        34.80                                                hydrogen    8.45         8.62                                                 nitrogen    12.56        12.37                                                chlorine    14.55        12.93                                                molar ratio 10:10:1:0    7:7:1:0                                              ______________________________________                                    

X-ray powder diffractometry was also performed on the resultingcrystalline sample and compared to samples of lysine monohydrate, lysinemonohydrochloride, succinic acid, and the 2:1:1:0 example of Turk. Thex-ray powder patterns of both lysine monohydrate and lysinemonohydrochloride (FIGS. 1 and 2, respectively) exhibit strongreflections in the 8-10 degree region of the diffractogram. Thediffractogram of succinic displays strong reflections at approximately20 and 26 degrees (FIG. 3). The pattern obtained from the subject of thecurrent invention is displayed in FIG. 4 and does not possess thefeatures of the starting materials shown in FIGS. 1, 2 and 3.Furthermore, upon comparison with the pattern obtained from the 2:1:1:0example of Turk (FIG. 5), the most intense features are not common,indicating the unique structure of the prepared crystalline material.

EXAMPLE 2

Solution Composition--2:1:1:0, Sodium/Potassium Free

The same procedure as Example 1 was used with 17.9 grams of L-lysinemonohydrate (0.109 moles) and 4.5 ml of concentrated hydrochloric acid(0.054 moles) instead of the two forms of lysine. A similar crystallineproduct was obtained and its x-ray powder pattern is shown in FIG. 6.

EXAMPLE 3

Solution Composition--2:2:1:1, Low Sodium

The procedure was reacted as in Example 1 with 12 grams (0.073 moles) ofL-lysine monohydrate dissolved in 20 ml of water to which 6.0 ml (0.073mole) of hydrochloric acid was added. Then 2.96 grams of disodiumsuccinate (0.018 mole) and 2.16 grams (0.018 mole) of succinic acid wereadded to the mixture. A crystalline product resulted with thecomposition shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Elemental analysis of Example 3 Solution composition-2:2:1:1                               weight %                                                         ______________________________________                                               carbon  33.12                                                                 hydrogen                                                                              8.46                                                                  nitrogen                                                                              11.99                                                                 chlorine                                                                              15.49                                                                 sodium  1.26                                                                  molar ratio                                                                           9:9:1:1.15                                                     ______________________________________                                    

X-ray powder patterns were collected for crystalline sodium chloride,the current example, and example 2:2:1:1 of Turk (FIGS. 7, 8 and 9,respectively). The current example did not display features of thestarting materials as shown in FIGS. 1, 2 and 3 nor does it possess acommon diffractogram with the example of Turk. It should also be notedthat the sodium content is only 1.26%.

EXAMPLE 4

Solution Composition--2:2:1:1, Low Potassium

The same procedure was used as in Example 3 except the 2.94 grams (0.018mole) of disodium succinate were replaced by 2.05 grams (0.036 mole) ofpotassium hydroxide. A similar crystalline product was obtained with itspowder pattern shown in FIG. 10.

EXAMPLE 5

Solution Composition--4:3:2:1, low potassium

The same procedure was used as in Example 1 except 2.04 grams (0.027mole) of potassium chloride were added. A similar crystalline productwas obtained with its elemental analysis given in Table 3 and its x-raypowder given in FIG. 11.

                  TABLE 3                                                         ______________________________________                                        Elemental analysis of Example 4 Solution composition-4:3:2:1                               weight %                                                         ______________________________________                                               carbon  33.57                                                                 hydrogen                                                                              8.60                                                                  nitrogen                                                                              11.89                                                                 chlorine                                                                              13.77                                                                 potassium                                                                             1.45                                                                  molar ratio                                                                           7:7:1:0.6                                                      ______________________________________                                    

EXAMPLE 6

Mixtures of Potassium Chloride with Example 1 Salt Product.

Potassium chloride is often used as a salty flavor to replace sodiumchloride. Unfortunately, potassium chloride has a strong metallic taste.Therefore, experiments were conducted to determine if the salty flavorof the current invention could be used to mask the metallic flavor ofthe potassium ion. Mixtures of potassium chloride and Example 1 withvarying weight percent were prepared by grinding.

The 2 to 5 wt % of KCl and Example 1 gave the best salty taste. KClconcentrations lower than 2% have little effect on the salty flavor,while higher concentrations increased the metallic taste. The results ofthis taste trials are presented in Table 4.

                  TABLE 4                                                         ______________________________________                                        Taste trials of KCl mixtures with Example 1                                   salt product at different wt % concentrations.                                Wt % KCl/Ex. 1      Powder taste                                              ______________________________________                                        100                 Irritates tongue                                           0                  Salty                                                      2                  Saltier                                                    5                  Saltier                                                   10                  Metallic-salty                                            32                  Metallic-salty                                            ______________________________________                                    

EXAMPLE 7

Comparison of the Taste of Different Examples of Salts of PresentInvention With One Another and With Other Existing Salt Products.

The salts of present invention and prior ones were tasted as solids andsolutions in water. Example salt solution concentrations of 4 to 70 wt %were tasted and 15 wt % solution found to best represent the saltytaste. Therefore, 15 wt % solutions of different salt products wereprepared, tasted, and compared.

The solid and solution tastes of similar salts appeared to be the same,but the solution gives a milder taste at 15 wt % concentration.

In summary, Examples 1 and 2 (Example 1 having better taste of salt thanExample 2) of the present invention with the same solution compositionresembles sodium chloride better than that of Turk. Example 3 of lowsodium tastes better than any other examples of salt products containingsodium or potassium. The summary of taste trial of different saltproducts are presented in Table 5.

                  TABLE 5                                                         ______________________________________                                        Summary of taste trials of different salt products                            Salt product                                                                              Molar ratio*     Taste*                                           ______________________________________                                        Table salt  N/A              Saltiest                                         Turk        2:2:1:1          Saltier+                                         Turk        2:1:1:0          Less salty                                       Ex. 1       2:1:1:0          Salty+                                           Ex. 2       2:1:1:0          Salty                                            Ex. 3       2:2:1:1          Saltier+                                         Ex. 4       2:2:1:1          Saltier                                          Ex. 5       4:3:2:1          Saltier                                          Ex. 6       2:1:1:1          Saltier                                          ______________________________________                                         *Aqueous starting solution composition molar ratios of Lys:Cl:Succ:Na or      K.                                                                            **Salty+, tastes better than salty.                                      

It is intended that the foregoing description be only illustrative ofthe present invention and that the present invention be limited only bythe hereinafter appended claims.

We claim:
 1. A process for the preparation of a crystalline compositionhaving the empirical formula:

    Lys.sub.a Cl.sub.b Succ.sub.c X.sub.d

wherein Lys is L-lysine, Succ is succinic ion and X is selected from thegroup consisting of a sodium and a potassium ion and wherein a isbetween about 3 to 10, wherein b is approximately the same as a, c is 1calculated as succinic acid, and d is 0 to 2 which comprises: (a)admixing lysine hydrochloride and a succinate compound selected from thegroup consisting of succinic acid and alkali metal salts thereof in amolar ratio of Lys to Succ calculated as succinic acid of about 2:1 inan aqueous solution until solution is near saturation; (b) heating thesolution at a temperature between about 60° C. and 80° C. and at areduced pressure such that water is removed from the solution; (c)cooling the solution so that the crystalline composition precipitatesfrom the solution; and (d) separating the crystalline composition fromthe solution.
 2. The process of claim 1 wherein X is hydrogen ion. 3.The process of claim 1 wherein X is potassium ion.
 4. The process ofclaim 1 wherein the X is sodium ion.
 5. The process of claim 1 wherein Xis sodium and potassium.
 6. The process of claim 1 wherein thetemperature is 70° C.
 7. The process of claim 1 wherein the lysinehydrochloride is prepared by reacting lysine monohydrate withhydrochloric acid.
 8. The process of claim 1 wherein the alkali metalsalt of succinic acid salts is prepared by reacting succinic acid withan alkali metal base.
 9. The process of claim 8 wherein X is sodium ion.10. The process of claim 8 wherein X is potassium ion.
 11. The processof claim 1 wherein lysine monohydrate is included with the lysinehydrochloride and wherein the lysine hydrochloride is lysinemonohydrochloride.